Meaning of “coo” - Learner’s Dictionary

coo

verb [ I ] us uk /kuː/ present participle cooing, past tense and past participle cooed
MAKE SOUND

to make a soft, low sound, like a pigeon (= large, grey bird)

SPEAK

to speak in a soft, low voice

(Definition of “coo” from the Cambridge Learner’s Dictionary © Cambridge University Press)